Manage your subscription

Science: Infrared speeds up the hunt for cervical cancer

By DAVID BRADLEY

Early detection of cervical cancer is crucial if the disease, which
is on the increase, is to be cured. Canadian and American researchers believe
they have developed a technique which should be quicker and more reliable
than traditional screening methods, such as the Pap smear test. By quickly
eliminating patients who definitely have no abnormal cells it could also
reduce the workload of clinics.

Teams headed by Patrick Wong at the Steacie Institute of Molecular Science,
Ottowa and Basil Rigas at Cornell University Medical College, New York,
based their screening process on infrared spectroscopy, which is used by
chemists to study the structure of molecules. The researchers say they can
identify the molecular changes which occur when cells become cancerous (Proceedings
of the National Academy of Sciences, vol 88, p 10988).

Wong and his colleagues carried out a study involving 156 women. Out
of these, 136 were deemed ‘normal’, while standard pathological techniques
revealed that 12 had cervical cancer and 8 had precancerous, or dysplastic,
cells.

The researchers measured the infrared absorption spectrum of cervical
samples from each woman. Infrared spectroscopy reveals the vibrational frequencies
characteristic of different chemical groups in a molecule. Complex molecules
give rise to absorption bands which are centred on these frequencies.

Advertisement

Wong’s team found that while the normal cervical samples had almost
identical spectra, the other 20 were very different. When the researchers
examined the samples known to contain malignant cells, they found that infrared
bands characteristic of glycogen had decreased dramatically in intensity,
indicating that less of the substance was present (see Diagram). Previous
research had shown that the level of glycogen, which is usually found at
high concentrations in cells of the vagina and liver, is reduced when abnormal
cells grow.

A second distinctive feature of the malignant samples was that the band
produced by so-called phosphodiester groups in DNA was much broader and
consisted of two overlapping bands. ‘The low-frequency component band is
due to so-called hydrogen bonding between DNA phosphodiester groups and
water molecules,’ says Wong.

The intensity of this low-frequency band increases dramatically in malignant
samples because in malignant cells a large number of phosphodiester groups
become hydrogen bonded to water, says Wong. The researchers found that in
dysplastic cells the degree of hydrogen bonding was halfway between that
of normal and malignant cells.

Wong claims that the present method of screening for cervical cancer,
the Pap test, is ‘not accurate’ and that ‘false negative and false positive
results can be more than 50 per cent’. He believes that the complicated
procedure of fixing and staining sample cells as well as the microscopic
examination and diagnosis by a cytologist is too subjective and is also
time-consuming and expensive. The researchers believe their technique is
more reliable and could reduce the burden on clinical laboratories.

The team is studying the possibility of extending the technique to detecting
other cancers, such as colon and liver cancer.